A challenge for the clinical neurologist is to decide which of the myriad patients with symptoms of dizziness, lightheadedness, or imbalance have a genuine vestibular disorder, be it peripheral or central. The clinical examination is often the key. A series of systematically applied, physiologically based maneuvers, designed to probe static and dynamic function of the vestibulo-ocular reflexes and the individual labyrinthine sensors, will almost always reveal the evidence of a vestibular system anomaly, which either clarifies the diagnosis or points to a need for a further evaluation. This chapter will describe these maneuvers and indicate their diagnostic usefulness. They include dynamic visual acuity, occlusive ophthalmoscopy, head impulse (rotational vestibulo-ocular reflex) and head heave (translational vestibulo-ocular reflex) testing, mastoid vibration-induced nystagmus (equivalent of a hot-water caloric stimulus in a patient with unilateral vestibular loss), hyperventilation-induced nystagmus (abnormal in fistula, craniocervical junction anomalies, compressive and demyelinating lesions, and cerebellar degenerations), Valsalva-induced nystagmus (abnormal in fistula and craniocervical junction anomalies), head-shaking–induced nystagmus (vertical nystagmus after horizontal head shaking points to a central disorder), positional nystagmus (lateral canal, posterior canal, central) and soundinduced nystagmus (superior canal dehiscence). When combined with a careful examination of eye alignment, gaze holding, saccade accuracy and speed, and smooth pursuit, a central or peripheral localization is usually possible. BASIC PHYSIOLOGICAL PRINCIPLES AND ANATOMICAL ORGANIZATION The clinical evaluation of the patient whose symptoms suggest vestibular dysfunction relies upon a solid understanding of vestibular physiology and anatomy and of the psychophysiological aspects of normal and abnormal vestibular sensation. The term vestibular will be used here in its broadest sense as the mechanism for detecting the attitude of the head with respect to gravity and to any movement of the head within the environment and also for generating the appropriate compensatory motor responses that assure clear vision and steady balance in response to movements of the head and body.